ShowSize on Windows Vista/7

Update: The following discussion applies not only to Windows Vista but to Windows 7 too.

I will attempt to explain why we had to discontinue the “Unused files report” starting with Windows Vista and why I advise not to use it even on earlier Windows systems now.

Vista breaks the “Unused Files” feature for NTFS:

On Vista, by default the “last access date” of the files are not updated on NTFS file systems. Microsoft did this to improve Vista performance on NTFS systems. The same is true of Windows 7.

This means that the above information is useless for all the files on NTFS volumes. There is a registry tweak possible so that Vista starts updating the “last access date” of files. But even then the information won’t be useful for quite some time. For example, if you switch on this feature now you will have to wait for at least 30 days of use to get a report that shows files not used in last 30 days. Hence, it’s not a good solution as there is no way for ShowSize to determine when the tweak was made. In other words, one can never rely on Unused column or the Unused Files report. Besides, this tweak might run into performance issues on Vista or later systems.

Corporate/LAN users, beware: If many Vista systems are using files on a shared NTFS volume, some will update the last access date and some won’t depending on whether they were fixed with the registry tweak. So on a shared volume, you can never be sure if the Unused Files report is useful at all.

THE HARD DECISION THAT WE MADE: Hence, it’s not possible to find a decent solution to this problem. We can at most give warning messages on Vista for NTFS volumes. But we can never be sure on shared volumes. Hence, starting with ShowSize version 5, we have entirely dropped this Unused Files report and the Used column in all the reports on Windows Vista, and later versions of Windows.